As the conductive polymer, polyaniline or the like are well known. In addition to its electrical properties, polyaniline has advantages that it can be synthesized relatively easily from inexpensive aniline and shows excellent stability to air or the like in the state in which it shows conductivity.
As the method for producing polyaniline, a method in which aniline or an aniline derivative is subjected to oxidative electropolymerization or chemical oxidative polymerization is known.
As for the oxidative electropolymerization, a method in which aniline is polymerized on an electrode is stated in Patent Document 1 or Patent Document 2. A film which is improved in electric properties or the like can be obtained in the oxidative electropolymerization. In general, oxidative electropolymerization is high in production cost as compared with chemical oxidative polymerization, and hence, is not suited to mass production. In addition, by oxidative electropolymerization, it is difficult to obtain a shaped body having a complex shape.
On the other hand, in order to obtain a conductive polymer such as aniline or an aniline derivative by chemical oxidative polymerization, a step in which a dopant (doping agent) is added to polyaniline in a non-conductive basic state (so-called Emeraldine base state) to conduct protonation is required. However, since polyaniline in a non-conductive basic state is hardly dissolved in most of organic solvents, it is not suited to industrial production. Further, a conductive polyaniline composite (so-called Emeraldine base state) generated after protonation is substantially not dissolved and not molten, and hence, it is difficult to produce a conductive composite material and its shaped body easily.
Under such circumstances, as a method for improving doping properties of polyaniline in the non-conductive basic state as well as for improving affinity for an inorganic solvent of conductive polyaniline after the doping, several methods have been proposed.
For example, Non-Patent Document 1 discloses that polyaniline exhibits excellent electric properties by using as a dopant a protonic acid which has affinity for an organic solvent such as dodecylbenzenesulfonic acid and camphorsulfonic acid (CSA). Patent Document 3 discloses a method in which polyaniline in the non-conductive basic state is dissolved in m-cresol using, for example, adamantanesulfonic acid as a dopant. Non-Patent Document 2 discloses a method in which polyaniline in the non-conductive basic state is doped in a specific solvent (a halogen-based strong acid) such as 2,2-dichloroacetic acid using 2-acrylamide-2-methyl-propanesulfonic acid as a dopant. Patent Document 4 discloses, as in the case of Non-Patent Document 2, discloses a method in which polyanilline in the non-conductive basic state is doped by using 2,2-dichloroacetic acid as a solvent and a di(2-ethylhexyl)ester of sulfosuccinic acid as a dopant.
However, a shaped body formed of conductive polyaniline obtained by the method disclosed in Patent Document Nos. 1 to 4 and Non-Patent Document Nos. 1 and 2 was not necessarily excellent in electric properties such as electric conductivity.
In order to improve the conductivity of a shaped body formed of conductive polyaniline, Patent Document 5 discloses a conductive polyaniline composition comprising a compound having (a) a substituted or unsubstituted polyaniline composite which has been protonated, which is dissolved in an organic solvent which is not substantially miscible with water, and (b) a phenolic hydroxyl group. Further, Patent Document 5 discloses that the amount of the (b) phenolic compound is normally 0.01 to 1000 mass %, preferably 0.5 to 500 mass %, relative to the amount of (a) the protonated substituted or unsubstituted polyaniline composite. Further, Patent Document 5 discloses a method in which polymerization of aniline is conducted by dissolving sodium diisooctyl sulfosuccinate and aniline in toluene, adding hydrochloric acid, cooling the flask on ice bath, and adding a solution obtained by dissolving ammonium persulfate in hydrochloric acid dropwise.
The reason that polymerization of aniline is conducted in the presence of hydrochloric acid in Patent Document 5 is that a higher degree of conductivity can be obtained when conductive polyaniline is synthesized in the presence of hydrochloric acid. Further, Non-Patent Document 3 discloses that the conductive polyaniline having a high molecular weight cannot be obtained as long as polymerization of aniline is conducted in the presence of hydrochloric acid.
In general, in a polymer material, there is a close relationship between the molecular weight and the material properties. For example, when a film is formed, the film strength is higher if a polymer material having a high molecular weight is used. As mentioned above, in polyaniline, an industrially advantageous material can be obtained when polymerization is conducted by using hydrochloric acid. On the other hand, in the field of electronic parts, chlorine-free materials are required since metal parts of electronic parts may corrode if materials containing chlorine is used and since the world-wide trend for reinforcement of environmental regulation has been strengthened in recent years. Hence, the dissolution-type polyaniline composite in Patent Document 5 has a problem that it has a high chlorine content.